Touch panel devices are widely used nowadays as an input means. A touch panel device comprises a touch panel sensor, a control circuit for identifying a contact position, wiring and a flexible printed circuit board (FPC). In many cases, a touch panel device is used as an input means for various devices (e.g., smartphones, ticket machines, ATM devices and gaming devices) having an incorporated display device such as a liquid crystal display or an organic EL display. In such devices, the touch panel sensor is disposed on a display panel of the display device, and as a result the touch panel device is able to receive input corresponding to a display image. A region of the touch panel sensor facing the display panel is transparent, and a region in which the contact position (proximity position) can be detected is referred to as an active area.
Touch panel devices fall into various categories based on the principle of detecting the contact position (proximity position). Capacitive coupling touch panel devices have become mainstream in recent times for a number of reasons, including optical brightness, design properties, structural simplicity, and also excellent functionality. In a capacitive coupling touch panel device, when an external conductor (a finger, stylus pen, etc.) for which the position is to be detected is placed in contact (proximity) through a dielectric material, parasitic capacitance produced by the external conductor is newly generated and the electrostatic capacity changes. The position of the external conductor on the touch panel sensor is detected by utilizing this change in electrostatic capacity. Capacitive coupling is further classified as surface or projected and attention is focusing on projected capacitive coupling because of compatibility with multitouch recognition (multipoint recognition) (e.g., JP 2007-533044 A).
FIG. 5 is a plan view illustrating the configuration of a display device equipped with a touch panel sensor (abbreviated below simply to “display device”, as appropriate) according to the prior art. It should be noted that drive electrodes 40 formed on a drive electrode surface 40S and sensing electrodes 50 formed on a sensing electrode surface 50S are shown in FIG. 5 in an exaggerated manner in order to help describe the arrangement of the drive electrodes 40 and the sensing electrodes 50. Furthermore, the drive electrodes 40 and sensing electrodes 50 are formed on one surface each of a transparent dielectric substrate 30, as will be described later, but electrode wires of both are shown in FIG. 5 in order to illustrate the positional relationship thereof.
As shown in FIG. 5, the display device is a laminate in which a touch panel 20 is bonded by means of a transparent adhesion layer on a display panel 10 such as a liquid crystal panel or an organic EL panel, and comprises a drive circuit for driving the touch panel 20. A display surface 10S is defined on a surface of the touch panel 10, and information such as images based on external signals is displayed on the display surface 10S.
The touch panel 20 is bonded by means of a cover layer 22 and a transparent adhesion layer 23. The transparent dielectric substrate 30 which is a constituent element of the touch panel 20 is overlaid in such a way as to cover the whole of the display surface 10S defined on the touch panel 10, and transmits the information displayed on the display surface 10S. The transparent dielectric substrate 30 is formed from a base material such as a transparent glass substrate or a transparent resin film, for example, and it may have a single-layer structure comprising one base material or it may have a multilayer structure in which two or more base materials are stacked.
A surface of the transparent dielectric substrate 30 on the side facing the display panel 10 (the rear side of the page=light source side) is set as the drive electrode surface 40S. A plurality of drive electrodes 40 and a plurality of drive terminal portions 43 are arranged along a Y direction on the drive electrode surface 40S with an interval (inter-drive-electrode region Sd) therebetween. Each of the plurality of drive electrodes 40 has a strip shape extending towards a drive electrode terminal portion 43 along an X direction orthogonal to the Y direction. Each of the drive electrodes 40 is separately connected to a selection circuit 34 via the drive electrode terminal portion 43, and is selected and driven as a result of receiving a signal.
A surface of the transparent dielectric substrate 30 on the opposite side to the display panel 10 (the front side of the page=viewing side) is set as the sensing electrode surface 50S. A plurality of sensing electrodes 50 and a plurality of sensing electrode terminal portions 53 are arranged along the X direction on the sensing electrode surface 50S with an interval (inter-sensing-electrode region Ss) therebetween. Each of the plurality of sensing electrodes 50 has a strip shape extending towards a sensing electrode terminal portion 53 along the Y direction. Each of the sensing electrodes 50 is separately connected to a detection circuit 35 via the sensing electrode terminal portion 53, and the voltage of each sensing electrode 50 is detected.
In FIG. 5, one drive electrode 40 (e.g., ND)/one sensing electrode 50 (e.g., NS) constitute a region in which electrostatic capacity is generated between the sensing electrode/drive electrode lying one over the other when seen in a plan view, and this is referred to as a node. The node constitutes a unit region for detecting an initial value of electrostatic capacity and a change in the electrostatic capacity resulting from contact with a human finger or the like. The size of the node (node size) is around several square millimeters and is expressed by the following equation.
Node size=size of active area of touch panel/number of pins in integrated circuit forming part of the touch panel
Furthermore, the display panel 10 comprises a color filter layer 15 in which a black matrix 15a is arranged along the X direction which is the direction of extension of the drive electrodes 40 and the Y direction which is the direction of extension of the sensing electrodes 50, the black matrix 15a having a structure defining a plurality of unit cells. Any of a red colored layer 15R for displaying a red color, a green colored layer 15G for displaying a green color, and a blue colored layer 15B for displaying a blue color is positioned in each unit cell defined by the black matrix 15a . A pixel width Cx along the X direction and a pixel width Cy along the Y direction are set at values commensurate with the resolution etc. of the display device.
Transparent materials comprising a metal oxide film such as zinc oxide, or a composite oxide film of a metal oxide including indium, tin, gallium and zinc etc., such as indium tin oxide (ITO) and indium gallium zinc oxide, are conventionally used for the drive electrodes and sensing electrodes employed in the touch panel sensor, and the material is typically ITO. However, these transparent materials have high resistance so there are problems in that this leads to a reduction in detection sensitivity when such materials are used in a touch panel having a large screen, and it has become necessary to use low-resistance materials. Electrodes having a configuration obtained by trimming a mesh formed by fine metal wires such as copper, aluminum or silver have come to be used as a result (e.g., JP 2013-156725 A).
In addition to being conductive in order to detect a change in electrostatic capacity, each of the plurality of electrodes forming part of the touch panel needs to be able to transmit light in such a way that there is no impediment to a viewer, since an image is displayed on the operating surface of the touch panel. That is to say, if the electrode wires of both the drive electrodes and the sensing electrodes comprise fine metal wires, this leads to a reduction in light transmittance when the surface area occupied by the electrode wires of the drive electrodes and the sensing electrodes increases when seen in a plan view.
In this regard, JP 5910761 B2 proposes a pattern designed by analyzing the pattern of the drive electrodes and the sensing electrodes in such a way that a mesh having rectangular units overall is constructed by placing the drive electrodes over the sensing electrodes when seen in a plan view. That is to say, by combining the pattern illustrated in FIG. 6a in which the drive electrodes 40 are arranged alongside each other, and the pattern illustrated in FIG. 6b in which the sensing electrodes 50 are arranged alongside each other, the mesh pattern shown in FIG. 7 is constructed, where the units have a rectangular shape (squares having one side α).
In FIG. 7, the sensing electrodes 50 (the pattern in FIG. 6b) depicted by line outlines are superimposed on the drive electrodes 40 (the pattern in FIG. 6a) depicted by black lines to construct a mesh pattern having rectangular units overall, and the electrodes, in which five main electrode wires (41, 51) and auxiliary electrode wires (42, 52) connecting the main electrode wires are arranged as a set, are defined by the inter-drive-electrode region Sd and the inter-sensing-electrode region Ss, and nodes N of 3 rows×3 columns are formed. Here, the auxiliary electrode wires of the drive electrodes/sensing electrodes lie over the main electrode wires of the sensing electrodes/drive electrodes, respectively. It should be noted that the auxiliary electrode wires serve to conduct the main electrode wires in each node to the drive electrode terminal portions 43 or the drive electrode terminal portions 53.
It should be noted that FIG. 7 shows the electrode pattern when dummy electrodes are not provided, but dummy electrodes may be formed between the arranged electrodes for the purpose of adjusting the change in electrostatic capacity or for the purpose of producing uniformity in a light/dark distribution within the screen, which occurs as the wiring becomes denser or finer. The dummy electrodes may also be referred to as floating, they are electrically independent and do not conduct with the electrodes, the dummy electrodes reduce parasitic capacitance between electrodes, and they prevent short circuiting produced by adjacent electrodes during high-frequency driving. It should be noted that the touch panel according to the present invention which will be described later may also be applied to an electrode pattern which comprises the dummy electrodes.
The main electrode wires forming the drive electrodes/sensing electrodes comprise electrode wires running diagonally down to the right/diagonally down to the left, and obliquely intersect the X direction and the Y direction, having an angle of inclination θd/θs in relation to the X axis. This is in order to avoid moiré(interference fringes) occurring as a result of interference with the black matrix 15a when the orientation of the electrode wires is close to the orientation of the pixels in the color filter layer 15 shown in FIG. 5. Moiréalso depends on the relationship of the black matrix 15a and the pitch (period) of the main electrode wires. Moiréis readily generated especially in the region of θd=θs=0°, 45° and 90°, so these angles are avoided, but FIG. 5 is depicted as θd=θs=45° for simplicity.
When the patterns of the drive electrodes and sensing electrodes are designed, a method in which the same pattern is provided in one node unit and the same pattern is repeated in proportion to the number of nodes, as shown in FIG. 5, while generation of moiréis avoided, involves the smallest data volume and the smallest design load.
However, as indicated above, the node size is determined by the size of the active area of the touch panel and the number of pins in the integrated circuit forming part of the touch panel, so it is not a simple matter to obtain design conditions (pitch and angle of inclination) enabling a repeat arrangement while avoiding moiré. Furthermore, conditions relating to moiréhave become more stringent due to the reduced size of nodes because of higher resolution in recent display devices, the increase in clear display devices that have not been subjected to antiglare treatment, and common design requirements for display devices having different resolutions, and there are an increasing number of cases in which it is becoming more difficult to find design conditions enabling repetition while avoiding moiré.
Meanwhile, in order to provide a design such that moiréis avoided without the use of a repeating arrangement, it is necessary to design the mesh pattern over the whole surface of the active area, so there are problems in that the data volume increases and the design load increases, which leads to higher costs and lower producibility.